jsp頁面異步獲取Controller數據JsonMappingException異常

使用JQuery向Controller異步獲取數據時，用json格式，Controller返回Map<String,Object>時報錯，首先看到的是

//此處錯誤貼得多一點，容易查
java.lang.IllegalStateException: Cannot call sendError() after the response has been committed
	at org.apache.catalina.connector.ResponseFacade.sendError(ResponseFacade.java:466)
	at org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolver.sendServerError(DefaultHandlerExceptionResolver.java:309)
	at org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolver.handleHttpMessageNotWritable(DefaultHandlerExceptionResolver.java:366)
	at org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolver.doResolveException(DefaultHandlerExceptionResolver.java:139)
	at org.springframework.web.servlet.handler.AbstractHandlerExceptionResolver.resolveException(AbstractHandlerExceptionResolver.java:136)
	at org.springframework.web.servlet.DispatcherServlet.processHandlerException(DispatcherServlet.java:1141)
	at org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:979)
	at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:933)
	at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:851)
	at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:953)
	at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:855)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:650)
	at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:829)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
	at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
	at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:88)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:106)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
	at org.springframework.orm.hibernate3.support.OpenSessionInViewFilter.doFilterInternal(OpenSessionInViewFilter.java:232)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:106)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:170)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
	at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:957)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:423)
	at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1079)
	at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:620)
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1753)
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1712)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
	at java.lang.Thread.run(Thread.java:722)

一開始認爲是 java.lang.IllegalStateException: Cannot call sendError() after the response has been committed  這個異常，也就是Controller作了屢次response，然而我代碼結構簡單，排除。

繼續往下翻，在日誌中看到：

com.fasterxml.jackson.databind.JsonMappingException: Infinite recursion (StackOverflowError) (through reference chain:

感受這纔是問題所在，因此度娘找到了這個博客 http://blog.csdn.net/cfydaniel/article/details/38820271，說是JSON的轉換問題，也就是JSON轉換內容的時候，出現了死循環致使溢出。緣由是個人List<Map<String,Object>>列表中含有對象，而且對象相互引用了。大概是這樣的：

UserInfo
private String username;
private String password;
private List<UserPhone> phoneList;
//......

UserPhone 
private String phone;
private String remark;
private UserInfo userInfo;
//......

List<Map<String,Object>> mapList = new ArrayList<Map<String,Object>>();
List<UserInfo> userList = 獲取到的不爲空的用戶列表；
for (UserInfo userInfo : userList) {
	Map<String,Object> tempMap = new HashMap<String,Object>();
	tempMap.put("username",username);
	tempMap.put("password",password);
	List<UserPhone> phoneList = userList.getUserList();//引用了UserPhone對象，其中又有UserInfo對象
	tempMap.put("phoneList",phoneList);
	mapList.add(tempMap);
}

//轉換mapList成json
//報錯

個人解決方法就是，不將UserPhone對象直接加進tempMap中，再次轉成String，也就不會報錯。

即：

List<Map<String,Object>> mapList = new ArrayList<Map<String,Object>>();
List<UserInfo> userList = 獲取到的不爲空的用戶列表；
for (UserInfo userInfo : userList) {
	Map<String,Object> tempMap = new HashMap<String,Object>();
	tempMap.put("username",userInfo.getUsername());
	tempMap.put("password",userInfo.getPassword());

	//phoneList
	List<UserPhone> userPhoneList = userList.getUserList();//引用了UserPhone對象，其中又有UserInfo對象
	List<Map<String,Object>> phoneList = new ArrayList<Map<String,Object>>();
	for (UserPhone userPhone : userPhoneList) {
		Map<String,Object> phoneTempMap = new HashMap<String,Object>();
		phoneTempMap.put("phone",userPhone.getPhone());
		phoneTempMap.put("remark",userPhone.getRemark());
		phoneList.add(phoneTempMap);
	}
	tempMap.put("phoneList",phoneList);
	mapList.add(tempMap);
}